Nitrogen (N) excretion and emissions can be reduced in fattening pigs by reducing dietary crude protein (CP) level. Effects of this strategy are well documented for moderate CP reduction, but little literature exists on further CP reduction made possible by free isoleucine, histidine, and leucine. This trial evaluated the effects of two levels of reduction in CP on growth performance, N balance, and gaseous emissions. Forty-eight pigs were allocated to 12 gaseous emission-measuring chambers at 28 kg live weight. Three dietary treatments (CTRL; −1.2pt; −2.4pt), with a CP content, respectively, of 18.1%, 16.9%, and 15.0% in phase 1 (28–48 kg) and 16.1%, 15.0%, and 13.8% in phase 2 (48–80 kg), were fed ad libitum. Growth performance was recorded for each phase. Body lipid and protein composition were analyzed by dual-energy X-ray absorptiometry in two animals per chamber at the beginning and end of the trial. These results were used to calculate the N balance. Slurry volume and composition were measured at the end of the trial. Ammonia, methane, and nitrous oxide emissions were recorded continuously. Data were analyzed with a general linear model including the linear and quadratic effect of CP reduction and phase as fixed effects. A trend for a quadratic effect of CP reduction on feed intake was observed (P = 0.085) with a decrease from CTRL to −1.2pt and then an increase with the −2.4pt treatment. Daily gain and gain to feed were improved by the low-CP diets in phase 1 but were degraded in phase 2 (phase × CP interaction, P < 0.001) while body composition was not affected. Nitrogen excretion decreased with CP reduction (linear effect, P = 0.023) but tended to plateau with the low-CP diets (quadratic effect, P = 0.081). Methane emissions per kg of gain were reduced with CP reduction (linear effect, P = 0.031). Ammonia emissions decreased with CP reduction, mostly in phase 1 (phase × CP interaction, P = 0.015); however, the emission factor (g N-NH3 / g urinary N) was not affected. Nitrous oxide emissions were not affected by CP reduction and its emission factor (g N-N2O / g N) tended to increase (linear effect, P = 0.07). Slurry ammonia-N decreased (linear effect, P < 0.023; quadratic effect, P = 0.049), but other slurry components were not significantly impacted. In this trial, a plateau in N excretion and emission reduction was reached with the −2.4pt treatment. Nevertheless, it is important to study such a reduction in conditions closer to commercial ones.

中文翻译：

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在生长猪日粮中减少粗蛋白的环境效益：是否值得进一步？


通过降低日粮粗蛋白 （CP） 水平，可以减少育肥猪的氮 （N） 排泄和排放。这种策略对中度降低 CP 的效果有据可查，但很少有文献证明游离异亮氨酸、组氨酸和亮氨酸可以进一步降低 CP。该试验评估了 CP 的两个水平降低对生长性能、氮平衡和气体排放的影响。48 头猪被分配到 12 个气态排放测量室，活重为 28 公斤。三种饮食处理 （CTRL;-1.2pt;-2.4pt），第一阶段 （28-48 kg） 的 CP 含量分别为 18.1%、16.9% 和 15.0%，第 2 阶段 （48-80 kg） 的 CP 含量分别为 16.1%、15.0% 和 13.8%，随意饲喂。记录每个阶段的生长表现。在试验开始和结束时，通过双能 X 射线吸收测定法分析每腔两只动物的体脂和蛋白质组成。这些结果用于计算 N 余额。在试验结束时测量浆液体积和成分。氨、甲烷和一氧化二氮排放被连续记录。使用一般线性模型分析数据，包括 CP 减少的线性和二次效应以及作为固定效应的相位效应。观察到 CP 减少对采食量的二次效应趋势 （P = 0.085），从 CTRL 降低到 -1.2pt，然后随着 -2.4pt 处理增加。在第 1 阶段，低 CP 饮食提高了日增重和饲料增重，但在第 2 阶段 （第 × 阶段 CP 相互作用，P < 0.001） 下降，而身体成分不受影响。氮排泄随着 CP 的减少而减少 （线性效应，P = 0.023），但在低 CP 饮食中趋于稳定 （二次效应，P = 0.081）。 每公斤增重的甲烷排放量随着 CP 的降低而减少（线性效应，P = 0.031）。氨排放随着 CP 的减少而减少，主要在第 1 阶段（阶段 × CP 相互作用，P = 0.015）;然而，发射因子 （g N-NH3 / g 尿 N） 不受影响。一氧化二氮排放不受 CP 减少的影响，其排放因子 （g N-N2O / g N） 趋于增加 （线性效应，P = 0.07）。浆液氨-N 减少（线性效应，P < 0.023;二次效应，P = 0.049），但其他浆料成分没有受到显著影响。在该试验中，-2.4pt 处理达到了氮排泄和减排的平台期。尽管如此，研究这种更接近商业条件的减少是很重要的。